Method and system for operating a fuel injector

ABSTRACT

Methods and systems for adjusting fuel injector operation according to changes in fuel pressure during inter-injection periods are described. The inter-injection period may be before and after fuel is injected to an engine. The methods and systems described herein may be suitable for direct and port fuel injectors.

FIELD

The present description relates generally to methods and systems foradjusting operation of fuel injectors that inject fuel to an internalcombustion engine.

BACKGROUND/SUMMARY

A fuel injector may be operated to precisely meter fuel flow to anengine cylinder. However, two injectors that are of a same type mayinject slightly different amounts of fuel even when commanded to deliverequal amounts of fuel. The differences in fuel injection amount may berelated to differences of materials used in manufacturing the fuelinjectors and component tolerances. One way to reduce the variance is todetermine how much fuel is injected by a fuel injector in response to afuel injection command. The amount of fuel that is injected may beestimated using a fuel pressure drop in a fuel rail. The amount of fuelthat the fuel injector injects may be corrected based on the pressuredrop in the fuel rail during a prior injection. While this approachremoves some error in the amount of fuel that is injected by a fuelinjector, there may still be opportunity for improvement.

In one example, the above issue may be addressed by a method foroperating a fuel injector, comprising: estimating a fuel pressure dropin a fuel rail due to injecting a fuel via a fuel injector according toan average fuel pressure before injecting the fuel, an average fuelpressure after injecting the fuel, a slope of fuel pressure during aninter-injection period before injecting the fuel, and a slope of fuelpressure during an inter-injection period after injecting the fuel; andadjusting fuel injected subsequently via the fuel injector based on theestimated fuel pressure drop.

By compensating for slopes of fuel pressure before and after a fuelinjection event, it may be possible to provide a technical result ofimproving accuracy of an amount of fuel that is injected by a fuelinjector to an engine. Specifically, fuel pressure changes within a fuelrail during inter-injection periods (e.g., periods when none of theengine's cylinders are injecting fuel) that may affect fuel flow througha fuel injector may be a basis for adjusting a fuel correction parameterthat may be applied to subsequent fuel injections so that amounts offuel injected may be closer to requested amounts of fuel to be injected.These sloped pressure changes that take place during the inter-injectionperiod may be related to thermal gain/loss in the fuel pressurizedwithin the fuel rail and not related to fuel injection.

The approach described herein may have several advantages. Inparticular, the approach may reduce errors in an amount of fuel that isinjected to an engine. Further, the approach compensates for fuelpressure changes in a fuel rail that may be due to thermal changes in afuel rail. In addition, the approach may be performed while a vehicle isoperating on a road.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an engine system;

FIG. 2 shows a schematic view of an example fuel system;

FIGS. 3 and 4 show graphic representations of fuel pressures that may becompensated according to the method of FIG. 5; and

FIG. 5 shows a high level flowchart of an example method forcompensating for pressure changes in a fuel system.

DETAILED DESCRIPTION

The following description relates to systems and methods for correctingamounts of fuel that are injected to an engine. In particular, requestedamounts of fuel to be injected may be adjusted according to pressurechanges in a fuel rail. The fuel injectors may be included in an engineof the type shown in FIG. 1. The fuel injectors may be part of a fuelsystem as shown in FIG. 2. Pressure changes during inter-injectionperiods that may affect an amount of fuel injected by a fuel injectorduring fuel injection are shown in FIGS. 3 and 4. Amounts of fuelinjected by a fuel injector may be compensated for inter-injectionpressure changes according to the method of FIG. 5.

Referring to FIG. 1, an internal combustion engine 10 is shown. Engine10 may be included in a drivetrain of a vehicle 100 configured foron-road propulsion. In one example, vehicle 100 is a hybrid electricvehicle. However, vehicle 100 may be a conventional vehicle thatincludes only an internal combustion engine as a source of propulsiveeffort.

Engine 10 comprising a plurality of cylinders, one cylinder of which isshown in FIG. 1, is controlled by electronic engine controller 12.Engine 10 is comprised of cylinder head 35 and block 33, which includecombustion chamber 30 and cylinder walls 32. Piston 36 is positionedtherein and reciprocates via a connection to crankshaft 40. Flywheel 97and ring gear 99 are coupled to crankshaft 40. An optional starter 96(e.g., low voltage (operated with less than 30 volts) electric machine)is included for cranking the engine during an engine start. The starter96 includes pinion shaft 98 and pinion gear 95. Pinion shaft 98 mayselectively advance pinion gear 95 to engage ring gear 99. Starter 96may be directly mounted to the front of the engine or the rear of theengine. In some examples, starter 96 may selectively supply torque tocrankshaft 40 via a belt or chain to initiate engine rotation during anengine start. Once a threshold engine speed is reached, the starter maybe decoupled from the engine and thereafter engine rotation ismaintained via fuel combustion in engine cylinders. In one example,starter 96 is in a base state when not engaged to the engine crankshaft.

Combustion chamber 30 is shown communicating with intake manifold 44 andexhaust manifold 48 via respective intake valve 52 and exhaust valve 54.Each intake and exhaust valve may be operated by an intake cam 51 and anexhaust cam 53. The position of intake cam 51 may be determined byintake cam sensor 55. The position of exhaust cam 53 may be determinedby exhaust cam sensor 57. Intake valve 52 may be selectively activatedand deactivated by valve activation device 59. Exhaust valve 54 may beselectively activated and deactivated by valve activation device 58.Valve activation devices 58 and 59 may be electro-mechanical devices.

Fuel injector 66 is shown positioned to inject fuel directly intocylinder 30, which is known to those skilled in the art as directinjection. Fuel injector 66 delivers liquid fuel in proportion to thepulse width from controller 12. Fuel is delivered to fuel injector 66 bya fuel system including a fuel tank 83, fuel pump 82, and fuel rail 80.Pressure in fuel rail 80 may be determined via pressure sensor 81. Inone example, a high pressure, dual stage, fuel system may be used togenerate higher fuel pressures. In further embodiments, fuel may bedelivered into an intake port of cylinder 30, upstream of intake valve52, to provide port injection of fuel. In still further embodiments, aportion of cylinder fuel may be delivered via direct injection while aremaining portion is delivered via port injection. The differentinjectors may deliver the same fuel or fuel of different properties,such as a gasoline fuel and an ethanol fuel.

Intake manifold 44 is shown communicating with turbocharger compressor162 and engine air intake 42. In other examples, compressor 162 may be asupercharger compressor. Shaft 161 mechanically couples turbochargerturbine 164 to turbocharger compressor 162. Optional electronic throttle62 adjusts a position of throttle plate 64 to control air flow fromcompressor 162 to intake manifold 44. Pressure in boost chamber 45 maybe referred to a throttle inlet pressure since the inlet of throttle 62is within boost chamber 45. The throttle outlet is in intake manifold44. In some examples, throttle 62 and throttle plate 64 may bepositioned between intake valve 52 and intake manifold 44 such thatthrottle 62 is a port throttle. Compressor recirculation valve (CRV) 47may be selectively adjusted to a plurality of positions between fullyopen and fully closed. Adjusting the opening of CRV 47 allows boostedintake air to be selectively recirculated to upstream of the compressorso as to decrease the pressure in boost chamber 45. Waste gate 163 maybe adjusted via controller 12 to allow exhaust gases to selectivelybypass turbine 164 to control the speed of compressor 162. Air filter 43cleans air entering engine air intake 42.

Distributorless ignition system 88 provides an ignition spark tocombustion chamber 30 via spark plug 92 in response to controller 12.Universal Exhaust Gas Oxygen (UEGO) sensor 126 is shown coupled toexhaust manifold 48 upstream of catalytic converter 70. Alternatively, atwo-state exhaust gas oxygen sensor may be substituted for UEGO sensor126.

Converter 70 can include multiple catalyst bricks, in one example. Inanother example, multiple emission control devices, each with multiplebricks, can be used. Converter 70 can be a three-way type catalyst inone example.

Controller 12 is shown in FIG. 1 as a conventional microcomputerincluding: microprocessor unit 102, input/output ports 104, read-onlymemory 106 (e.g., non-transitory memory), random access memory 108, keepalive memory 110, and a conventional data bus. Controller 12 is shownreceiving various signals from sensors coupled to engine 10, in additionto those signals previously discussed, including: engine coolanttemperature (ECT) from temperature sensor 112 coupled to cooling sleeve114; a position sensor 134 coupled to an driver demand pedal 130 forsensing force applied by foot 132; a position sensor 154 coupled tobrake pedal 150 for sensing force applied by foot 152, a measurement ofengine manifold pressure (MAP) from pressure sensor 122 coupled tointake manifold 44; an engine position sensor from a Hall effect sensor118 sensing crankshaft 40 position; a measurement of air mass enteringthe engine from sensor 120; and a measurement of throttle position fromsensor 68. The propulsive effort pedal and brake pedal may be combinedfor example in a pivoting setup to select either increasing vehiclespeed or decreasing vehicle speed. Further, the propulsive effort pedalmay be combined with the transmission direction selection for example,joystick control. Barometric pressure may also be sensed (sensor notshown) for processing by controller 12. In a preferred aspect of thepresent description, engine position sensor 118 produces a predeterminednumber of equally spaced pulses every revolution of the crankshaft fromwhich engine speed (RPM) can be determined.

The controller 12 receives signals from the various sensors of FIG. 1and employs the various actuators of FIG. 1, such as throttle 62, fuelinjector 66, spark plug 92, etc., to adjust engine operation based onthe received signals and instructions stored on a memory of thecontroller. As one example, the controller may send a pulse width signalto the fuel injector to adjust an amount of fuel delivered to acylinder. Further, controller 12 may receive input from a human operatoror vehicle passenger via human/machine interface 195. Human/machineinterface may be a touch screen, touch panel, key switch, or other knowninput device.

During operation, each cylinder within engine 10 typically undergoes afour stroke cycle: the cycle includes the intake stroke, compressionstroke, expansion stroke, and exhaust stroke. During the intake stroke,generally, the exhaust valve 54 closes and intake valve 52 opens. Air isintroduced into combustion chamber 30 via intake manifold 44, and piston36 moves to the bottom of the cylinder so as to increase the volumewithin combustion chamber 30. The position at which piston 36 is nearthe bottom of the cylinder and at the end of its stroke (e.g., whencombustion chamber 30 is at its largest volume) is typically referred toby those of skill in the art as bottom dead center (BDC).

During the compression stroke, intake valve 52 and exhaust valve 54 areclosed. Piston 36 moves toward the cylinder head so as to compress theair within combustion chamber 30. The point at which piston 36 is at theend of its stroke and closest to the cylinder head (e.g., whencombustion chamber 30 is at its smallest volume) is typically referredto by those of skill in the art as top dead center (TDC). In a processhereinafter referred to as injection, fuel is introduced into thecombustion chamber. In a process hereinafter referred to as ignition,the injected fuel is ignited by known ignition means such as spark plug92, resulting in combustion.

During the expansion stroke, the expanding gases push piston 36 back toBDC. Crankshaft 40 converts piston movement into a rotational torque ofthe rotary shaft. Finally, during the exhaust stroke, the exhaust valve54 opens to release the combusted air-fuel mixture to exhaust manifold48 and the piston returns to TDC. Note that the above is shown merely asan example, and that intake and exhaust valve opening and/or closingtimings may vary, such as to provide positive or negative valve overlap,late intake valve closing, or various other examples.

In some examples, vehicle 100 may be a hybrid vehicle with multiplesources of torque available to one or more vehicle wheels 155. In otherexamples, vehicle 100 is a conventional vehicle with only an internalcombustion engine, or an electric vehicle with only electric machine(s).In the example shown, vehicle 100 includes engine 10 and an electricmachine 153. Electric machine 153 may be a motor or a motor/generator.Crankshaft 40 of engine 10 and electric machine 153 are connected via atransmission 157 to vehicle wheels 155. In the depicted example, a firstclutch 156 is provided between crankshaft 40 and electric machine 153.Electric machine 153 is shown directly coupled to transmission 157.Controller 12 may send a signal to an actuator of each clutch 156 toengage or disengage the clutch, so as to connect or disconnectcrankshaft 40 from electric machine 153 and the components connectedthereto, and/or connect or disconnect electric machine 153 fromtransmission 157 and the components connected thereto. In otherexamples, clutches need not be included. Transmission 157 may be agearbox, a planetary gear system, or another type of transmission. Thepowertrain may be configured in various manners including as a parallel,a series, or a series-parallel hybrid vehicle.

Electric machine 153 receives electrical power from a traction battery158 to provide torque to vehicle wheels 155. Electric machine 153 mayalso be operated as a generator to provide electrical power to chargebattery 158, for example during a braking operation.

Referring now to FIG. 2, a detailed illustration of a fuel system thatsupplies fuel to an engine is shown. The fuel system of FIG. 2 may bemonitored and controlled in the engine system of FIG. 1 via the methodof FIG. 5.

Fuel system 200 includes various valves and pumps that are controlled bycontroller 12. Fuel pressure in fuel rail 80 is sensed via pressuresensor 81. Controller 12 controls pressure in fuel rail 80 usingpressure feedback from pressure sensor 81. Controller 12 activates lowpressure fuel pump 206 to supply fuel to fuel pump flow metering valve208 and optional port fuel injectors 67. Fuel pump flow metering valve208 controls the amount of fuel entering high pressure fuel pump 82.Thus, pressure in fuel rail 80 may be adjusted via adjusting a positionof metering valve 208. Cam 216 is driven by the engine 10 (of FIG. 1)and it provides motive force to piston or plunger 202 which operates onfuel in pump chamber 212.

High pressure fuel pump 82 directs fuel to fuel injector rail 80 viacheck. Fuel pressure in fuel rail 80 may be controlled via adjustingvalve 208. Fuel rail 80 may provide fuel to one cylinder bank of anengine via direct fuel injectors 66.

Low pressure fuel pump 206 may also supply fuel to fuel rail 250. Portfuel injectors 67 may be supplied fuel via fuel rail 250. Pressure infuel rail 250 may be determined via pressure sensor 251. Fuel that isnot injected during an engine cycle may be returned to fuel tank 83.

As such, fuel controls such as fuel injection timing and an amount offuel injected may account for a difference between a scheduled fuelpulse width that is computed based on a last update of cylinder aircharge estimate and a fuel pulse width realized. The pressure of thefuel rail 80 may vary over the course of an injection event with thepressure increasing during a stroke of the high pressure fuel pump 82and then decreasing as fuel is delivered from the direct injectors 66.Therefore, there may be a change in fuel rail pressure between the timeof scheduling of a fueling event and the actual fuel injection. Thispressure difference may lead to less reliable estimations of an amountof fuel injected. Inaccurate estimation of a difference between arequested amount of fuel injected and an actual amount of fuel injected(fueling difference) may result in inaccuracies in future injectionevent scheduling.

After a first injection of fuel to a cylinder via a direct fuel injector66 coupled to the cylinder and before a second injection of fuel to thecylinder, a pressure in the fuel rail 80 coupled to the direct fuelinjector 66 may be sampled via controller 12. Upon completion of thefirst injection of fuel to the cylinder, a fueling amount (mass orvolume) difference for the first injection may be estimated based on achange in pressure in the fuel rail during the first injection, and asecond injection of fuel to the cylinder via the direct fuel 66 injectormay be scheduled based on the prior fueling difference which may be anexcess or a deficit. Scheduling the second injection of fuel may includescheduling a time of initiation of the second injection and an amount offuel to be injected during the second injection based on the fuelingdifference. The second injection of fuel may be carried out immediatelysucceeding the first injection of fuel without any injection events forthe cylinder in between. The fueling difference may be estimated as adifference between an expected amount of fuel delivered to the cylinderduring the first injection and an actual amount of fuel delivered to thecylinder during the first injection. The expected amount of fueldelivered may be a function of the change in pressure in the fuel rail80 during the first injection. In one example, the change in pressuremay be determined as described in detail with regard to FIG. 5.

Thus, the system of FIGS. 1 and 2 provides for an engine system,comprising: an engine including a fuel injector; and a controller withcomputer readable instructions stored on non-transitory memory that whenexecuted cause the controller to: adjust an amount of fuel injected by afuel injector in response to a change in fuel pressure in a fuel railbefore a preceding fuel injection by the fuel injector and in responseto a change in fuel pressure after the preceding fuel injection by thefuel injector. The engine system includes where the change in fuelpressure in the fuel rail before the preceding fuel injection is duringan inter-injection period immediately before the preceding fuelinjection. The system includes where the change in fuel pressure in thefuel rail after the preceding fuel injection is during aninter-injection period immediately following the preceding fuelinjection.

In some examples, the engine system further comprises additionalinstructions to estimate the change in fuel pressure according to anaverage fuel pressure before the preceding fuel injection, and anaverage fuel pressure after the preceding fuel injection injecting thefuel. The engine system includes where the change in fuel pressurebefore the preceding fuel injection is based on a slope of fuel pressureduring an inter-injection period before the preceding fuel injection.The engine system includes where the change in fuel pressure after thepreceding fuel injection is based on a slope of fuel pressure during aninter-injection period after the preceding fuel injection. The enginesystem further comprises additional instructions that cause thecontroller to estimate the change in fuel pressure based on a halfperiod of the inter-injection period before the preceding fuelinjection. The engine system further comprises additional instructionsthat cause the controller to estimate the change in fuel pressure basedon a half period of the inter-injection period after the preceding fuelinjection.

The present description provides a way to return an accurate pressuredrop due to injection in the presence of a “pressure slope” due tothermal gain/loss in the fuel rail. Left unaccounted, a down slope(e.g., negative slope) makes the fuel pressure drops appear larger thanactual and an up slope (e.g., positive slope) makes the fuel pressuredrops look smaller than actual. The inventors have observed thatfollowing soon after a pump stroke, the fuel pressure slope is negative.Shortly before another pump stroke occurs, the fuel pressure slope ispositive. Such conditions if unaccounted may have the potential to behighly deleterious to PBIB's purpose of balancing injectors.

Referring now to FIG. 3, a plot that graphically illustrates how apressure drop due to injection of fuel may be distinguished from a fuelpressure change that may be due to heating and cooling within a fuelrail is shown. Plot 300 includes a vertical axis and a horizontal axis.The vertical axis represents pressure in a fuel rail, or fuel railpressure, and pressure within the fuel rail increases in the directionof the vertical axis arrow. The horizontal axis represents time and timeincreases from the left side of the figure to the right side of thefigure. Trace 302 represents pressure in a fuel rail. The sequence ofFIG. 3 may be provided by raising pressure in fuel rail to apredetermined threshold pressure, deactivating the high pressure fuelpump after pressure in the fuel rail reaches the threshold pressure,then injecting fuel sequentially into the engine according to theengine's firing order. Each time fuel is injected, pressure in the fuelrail falls since less fuel is held in the fuel rail.

At time t0, a fuel injection by a fuel injector completes (not shown)and pressure in the fuel rail begins to gradually decrease due tocooling of the fuel rail. The time between time t0 and time t1 is aninter-injection time where fuel is not injected to the engine. Theamount of time between time t0 and t1 is an inter-injection period. Onehalf of the inter-injection period is indicated at 320. The averagepressure in the fuel rail between time t0 and time t1 is the pressure at304. The fuel pressure at 304 may be referred to as an average precedinginter-injection pressure and it may be denoted as: p_(i) .

At time t1, fuel is injected to the engine and the fuel rail pressuredrops due to fuel leaving the fuel rail and the fuel rail not beingsupplied with additional fuel. The time between time t1 and time t2 is asecond inter-injection time where fuel is not injected to the engine.The time between time t1 a time t2 may also be referred to as aninter-injection period and the inter-injection period is indicated at316. The actual fuel pressure drop that is due to the fuel injection attime t1 is indicated at 310 and it may be denoted as: δp_(i) ^(T).Additionally, there is a fuel pressure drop between the averageinter-injection period pressure at 304 and fuel pressure at thebeginning of fuel injection at time t1. The fuel pressure drop betweenthe average inter-injection period pressure at 304 and the fuel pressureat the beginning of fuel injection at time t1 is indicated by thedistance at 312 and it may be denoted as:

${{- \alpha_{i}} \cdot \frac{T}{2}},$where α_(i) is the slope of pressure indicated by trace 302 between 304and time t1. T/2 is the half inter-injection period indicated at 320.The slope of a particular inter-injection period may be determined via aleast squares fit to the fuel rail pressure versus inter-injection timevia the following equation:

${{slope} = \frac{( {\sum\limits_{k = 1}^{n}\;{t_{k}P_{k}}} ) - ( {n \cdot \overset{\_}{t} \cdot \overset{\_}{P}} )}{{\sum\limits_{k = 1}^{n}\; t_{k}^{2}} - {n \cdot t^{- 2}}}},$where n is the total number of data pairs in the relationship betweenfuel rail pressure and inter-injection time, t_(k) is theinter-injection time for the k^(th) sample, and P_(k) is the fuel railpressure for the k^(th) sample. Alternatively, the slope may bedetermined via other known methods.

At time t2, fuel is injected to the engine again and the fuel railpressure drops again. The plot ends shortly after time t2. The averageinter-injection fuel pressure between time t1 and time t2 is indicatedat 305. Half of the subsequent inter-injection period is indicated at318. The fuel pressure drops between the fuel pressure at the end offuel injection at time t1 and the average subsequent inter-injectionfuel pressure indicated at 305. The fuel pressure at 305 may be referredto as an average subsequent inter-injection pressure and it may bedenoted as: p_(i+1) . The pressure drop between time t1 and the averageinter-injection fuel pressure indicated at 305 is indicated by thedistance at 314 and it may be denoted as:

${{- \alpha_{i + 1}} \cdot \frac{T}{2}},$where α_(i+1) is the slope of the subsequent pressure drop indicated bytrace 302 between time t1 and 305. T/2 is the half inter-injectionperiod indicated at 318.

The actual pressure drop for the fuel injection at time t1 may beexpressed via the following equation:

${{\delta\; p_{i}^{T}} = {\overset{\_}{p_{i}} - \overset{\_}{p_{i + 1}} + {\alpha_{i}\frac{T}{2}} + {\alpha_{i + 1}\frac{T}{2}}}},$where the variables are as previously described. Accordingly, the actualpressure drop due to injecting fuel may be determined from the averageinter-injection fuel pressures before and after the fuel injection, theslopes of fuel pressure before and after fuel injection, and theinter-injection period T.

Referring now to FIG. 4, a plot that graphically illustrates how apressure drop due to injection of fuel may be distinguished from a fuelpressure change that may be due to heating and cooling within a fuelrail according to a second method is shown. Fuel pressure in a fuel railmay oscillate for a short time before and a short time after fuel isinjected via a fuel injector. The oscillations may make it moredifficult to process average fuel pressures and slopes of fuel railpressure during inter-injection periods. Therefore, it may be desirableto exclude a short time before a fuel injection and a short time afterfuel injection from fuel pressure that is applied to determine an actualpressure drop due to fuel injection. FIG. 4 illustrates how a timebefore and a time after fuel is injected into the engine may be excludedfrom estimating a pressure drop in a fuel rail that is due to fuelinjection.

Similar to plot 300, plot 400 includes a vertical axis and a horizontalaxis. The vertical axis represents pressure in a fuel rail or fuel railpressure and pressure within the fuel rail increases in the direction ofthe vertical axis arrow. The horizontal axis represents time and timeincreases from the left side of the figure to the right side of thefigure. Trace 402 represents pressure in a fuel rail. The sequence ofFIG. 4 may be provided by raising pressure in fuel rail to apredetermined threshold pressure, deactivating the high pressure fuelpump after pressure in the fuel rail reaches the threshold pressure,then injecting fuel sequentially into the engine according to theengine's firing order. Each time fuel is injected, pressure in the fuelrail falls since less fuel is held in the fuel rail.

At time t10, a fuel injection by a fuel injector completes (not shown)and pressure in the fuel rail begins to gradually decrease due tocooling of the fuel rail. The time between time t10 and time t11 is aninter-injection time where fuel is not injected to the engine. Theamount of time between time t10 and t11 is an inter-injection period. Asubsequent time after the injection at time t10 where it may bedesirable to exclude fuel pressure data from the estimate of the fuelpressure drop at time t11 is indicated at 432 and this time may bedenoted as x. A preceding time before the injection at time t11 where itmay be desirable to exclude fuel pressure data from the estimate of thefuel pressure drop at time t11 is indicated at 430 and this time may bedenoted as y. The average pressure in the fuel rail between time (t10+x)and time (t11−y) is the pressure at 404 (404 is halfway in between time(t10+x) and time (t11−y)). The fuel pressure at 404 may be referred toas a preceding inter-injection pressure and it may be denoted as p_(i) .The duration from 404 to time t11 is indicated at 420.

At time t10, fuel is injected to the engine and the fuel rail pressuredrops due to fuel leaving the fuel rail and the fuel rail not beingsupplied with additional fuel. A subsequent time after the injection attime t11 where it may be desirable to exclude fuel pressure data fromthe estimate of the fuel pressure drop at time t11 is indicated at 432and this time may be denoted as x. A preceding time before the injectionat time t12 where it may be desirable to exclude fuel pressure data fromthe estimate of the fuel pressure drop at time t11 is indicated at 430and this time may be denoted as y. The time between time t11 and timet12 is a second inter-injection time where fuel is not injected to theengine. The time between time t11 a time t12 may also be referred to asan inter-injection period and the inter-injection period is indicated at416. The actual fuel pressure drop that is due to the fuel injection attime t11 is indicated at 410 and it may be denoted as δp_(i) ^(T).Additionally, there is a fuel pressure drop between the averageinter-injection period pressure at 404 and fuel pressure at thebeginning of fuel injection at time t11. The fuel pressure drop betweenthe average inter-injection period pressure at 404 and the fuel pressureat the beginning of fuel injection at time t11 is indicated by thedistance at 412 and it may be denoted as

${{- \alpha_{i}} \cdot \frac{( {T - x + y} )}{2}},$where α_(i) is the slope of pressure indicated by trace 402 between 404and time t11 (fuel rail pressure samples between 404 and time (t11−y)may be used to compute the slope α_(i)). T is the inter-injectionperiod, x is as previously described, and y is as previously described.The duration indicated by 420 is equal to (T−x+y)/2.

At time t12, fuel is injected to the engine again and the fuel railpressure drops again. The plot ends shortly after time t12. The averageinter-injection fuel pressure between time (t11+x) and time (t12−y) isindicated at 405 (405 is halfway in between time (t11+x) and time(t12−y)). The duration from t11 to time 405 is indicated at 418. Thefuel pressure drops between the fuel pressure at the end of fuelinjection at time t11 and the average inter-injection fuel pressureindicated at 405. The fuel pressure at 405 may be referred to as anaverage preceding inter-injection pressure and it may be denoted as:P_(i+1) . The pressure drop between time t11 and the averageinter-injection fuel pressure indicated at 405 is indicated by thedistance at 414 and it may be denoted as

${{- \alpha_{i + 1}} \cdot \frac{( {T + x - y} )}{2}},$where α_(i+1) is the slope of the subsequent pressure drop indicated bytrace 402 between time t11 and 405 (fuel rail pressure samples betweentime (t11+x) and time 405 may be used to compute the slope α_(i+1)). Tis the inter-injection period, x is as previously described, and y is aspreviously described. The duration indicated by 418 is equal to(T+x−y)/2.

The actual pressure drop for the fuel injection at time t11 may beexpressed via the following equation:

${{\delta\; p_{i}^{T}} = {\overset{\_}{p_{i}} - \overset{\_}{p_{i + 1}} + {\alpha_{i}\frac{( {T - x + y} )}{2}} + {\alpha_{i + 1}\frac{( {T + x - y} )}{2}}}},$where the variables are as previously described. Accordingly, the actualpressure drop due to injecting fuel may be determined from the averageinter-injection fuel pressures before and after the fuel injection, theslopes of fuel pressure before and after fuel injection, theinter-injection period T, and times x and y where fuel rail pressuredata is disregarded and not used to determine the drop in fuel pressurein the fuel rail.

Referring now to FIG. 5, a high level flow chart of an example method500 for adjusting operation of a fuel injector is shown. The method ofFIG. 5 may be incorporated into the system of FIGS. 1 and 2 asexecutable instructions stored in controller non-transitory memory. Inaddition, other portions of method 500 may be performed via a controllertransforming operating states of devices and actuators in the physicalworld. The controller may employ engine actuators of the engine systemto adjust engine operation.

At 502, method 500 determines operating conditions. The engine andvehicle operating conditions may be determined via the sensors andactuators described herein. In one example, the operating conditions mayinclude but are not limited to ambient temperature, ambient pressure,engine temperature, engine speed, vehicle speed, fuel rail pressure, anddriver demand pedal position. Method 500 proceeds to 504.

At 504, method 500 judges if conditions are present for performingpressure based fuel injector balancing. In one example, pressure basedfuel injector balancing may be performed during conditions where enginetemperature is greater than a threshold temperature and driver demandtorque or power is less than a threshold. If method 500 judges thatconditions are present to perform pressure based fuel injectorbalancing, the answer is yes and method 500 proceeds to 506. Otherwise,the answer is no and method 500 proceeds to 515. In another examplecondition, PBIB test pulses may be issued where normally the enginecontroller would call for only PFI and no DI operation. In this way, theDI injection amount may not be inadvertently reduced should it be neededfor charge cooling or pre-ignition prevention.

At 506, method 500 begins to perform pressure based fuel injectorbalancing. Pressure based fuel injector balancing may be performedaccording to the method described in U.S. Pat. No. 7,717,088 which ishereby fully incorporated by reference.

The controller runs a calibration injection sequence for a predeterminedK number of times (e.g., 3 times). The routine may also predetermine theorder in which injectors are to be activated in the calibrationinjection sequence. It may determine when and how many times eachinjector may be activated (e.g., opened from a closed position) during acalibration injection sequence. It may further include a countingmechanism to keep track of the activation of injectors and make surefuel injection is cycled through all injectors before proceeding to thenext calibration injection sequence. For example for a 4-cylinderengines with 4 injectors, the routine may predetermine that calibrationwill proceed in the following sequences for a calibration injectionsequence: injector #1, #2 #3, #4 and the calibration injection sequencemay be repeated 3 times in a fuel injector calibration routine. Theroutine may also determine that the fuel injector calibration routinemay be repeated after a predetermined amount of time has elapsed (e.g.,10 min) after the conclusion of the last Fuel Injector CalibrationRoutine.

The control unit may run a fuel injector correction coefficientdetermining routine for each injector. For example, if the engine is afour cylinder engine and each engine has one injector, the fuel injectorcorrection coefficient determining routine may be run four times, oncefor each injector.

The controller 12 requests the high pressure fuel supply pump (e.g., 82)to issue extra pump strokes, increase pump stroke frequency, and/orincrease a pump stroke for at least one stroke so that the fuel pressurein the high pressure fuel rail (e.g., 80) reaches a predetermined targetcalibration pressure (P_(m)). Method 500 proceeds to 508.

At 508, method 500 12 turns off the high pressure fuel supply pump 82 sothat no more fuel will be further supplied to the high pressure fuelrail 80 via fuel pump 82. Method 500 proceeds to 510.

At 510, method runs a series of fuel injections in a predeterminedsequence (e.g., injector #1, injector #2, injector #3, injector #4, orin a firing order as prescribed for the engine) and repeat the sequencefor a predetermined L number of times (e.g., 3 engine cycles, where eachinjector operates at least once during each engine cycle) whilemonitoring the fuel pressure (P) profile as a function of time orinjection events in the fuel rail. Each of the fuel injections may becommanded to provide predetermined fuel injector pulse widths. Theinjection series may be schedules so that at the end of the injections,P reaches or falls below a normal operating target pressure (P_(n)),where P_(n) is a desired target fuel pressure for the high pressure fuelreserve during normal fuel injection events. In some examples, theroutine may monitor the fuel pressure in the high pressure fuel rail 80.The routine may also return the fuel pressure in the high pressure fuelrail back to a normal operating target pressure (P_(n)) before the startof the next calibration injection sequence, based on operatingconditions, which may include engine operating conditions. Method 500proceeds to 512.

At 512, method 500 calculates fuel pressure drop (δp_(i jk) ^(T)) due toeach injection by the j^(th) injector (e.g., k=1, 2, 3 . . . 9 if eachinjector is injected 3 times during a calibration injection cycle andthe calibration injection cycle is run 3 times during a calibrationevent). δp_(i jk) ^(T) corresponds to pressure drop in the high pressurefuel reserved due to injection by j^(th) injector during the k^(th)injection. Various engine operating conditions or events may affect fuelrail pressure measurements and may be taken into consideration whencalculating the fuel pressure drop (δp_(i jk) ^(T)) attributed to eachinjection. In one example, the fuel pressure drop for a single injectionof fuel may be determined via a first equation:

${{\delta\; p_{i}^{T}} = {\overset{\_}{p_{i}} - \overset{\_}{p_{i + 1}} + {\alpha_{i}\frac{T}{2}} + {\alpha_{i + 1}\frac{T}{2}}}},$where the variables are as previously described. Alternatively, the fuelpressure drop may be determined via a second equation:

${{\delta\; p_{i}^{T}} = {\overset{\_}{p_{i}} - \overset{\_}{p_{i + 1}} + {\alpha_{i}\frac{( {T - x + y} )}{2}} + {\alpha_{i + 1}\frac{( {T + x - y} )}{2}}}},$where the variables are as previously described. Method 500 proceeds to514.

At 514, method 500 calculates an amount of fuel actually injected ineach injection Q_(jk), using the following equation:Q _(jk) =δp _(i) _(jk) ^(T) /C

where C is a predetermined constant coefficient for converting theamount of fuel pressure drop to the amount of fuel injected. In oneexample, C may be a function of fuel rail volume, effective bulk modulusof the fuel, and density of the fuel.

Method 500 may also determine an average amount of fuel actuallyinjected by injector j (Q_(j)) using the following equation:

$Q_{j} = {( {\sum\limits_{k = 1}^{k_{\max}}\; Q_{jk}} )/k_{\max}}$

where k is number of injections by injector j (e.g., k=1, 2, 3 . . . 9if each injector is injected 3 times during a calibration injectioncycle and the calibration injection cycle is run 3 times during acalibration event), and k_(max) is the largest k value (e.g., k_(max)=9if each injector is injected 3 times during a calibration injectioncycle and the calibration injection cycle is run 3 times during acalibration event).

Method 500 may determine correction factors for each fuel injector. Inone example, method 500 may determine the correction factor via thefollowing equation:Injcor_(j)=β(reqInj_(j) −Q _(j))

where Injcor_(j) is the injector fuel injection correction amount forthe j^(th) injector, β is a gain factor that may vary between 0 and 1,reqInj_(j) is the amount of fuel that was requested to be injected bythe i^(th) injector during the injector calibration sequence, and Q_(j)is the average amount of fuel injected by the j^(th) injector during theinjector calibration sequence. Of course, in other examples, thecorrection factors may be determined in alternative ways. Method 500stores the correction factors in controller memory. Method 500 proceedsto 516.

At 516, method 500 may adjust requested amounts of fuel to be injectedby the injection correction factors determined at 514. In one example,an amount of fuel that is requested to be injected may be multiplied bythe fuel injector correction factor for the corresponding fuel injectorthat is scheduled to inject the requested amount of fuel to determine anadjusted fuel injection amount for a particular cylinder. Method 500injects fuel amounts to the engine that are corrected via the correctionfactors.

At 515, method 500 retrieves fuel injection correction factors fromcontroller memory that serve as a basis for correcting the amount ofrequested fuel to be injected to the engine cylinders. Method 500proceeds to 516.

In this way, the method of FIG. 5 may adjust fuel injection amountsaccording to correction factors that are based on a pressure drop thatis observed in a fuel rail. The pressure drop may be converted into afuel mass and the fuel mass that is actually injected may be the basisfor correcting an amount of fuel that is actually injected.

Thus, the method of FIG. 5 provides for a method for operating a fuelinjector, comprising: estimating a fuel pressure drop in a fuel rail dueto injecting a fuel via a fuel injector according to an average fuelpressure before injecting the fuel, an average fuel pressure afterinjecting the fuel, a slope of fuel pressure during an inter-injectionperiod before injecting the fuel, and a slope of fuel pressure during aninter-injection period after injecting the fuel; and adjusting fuelinjected subsequently via the fuel injector based on the estimated fuelpressure drop. The method further comprises estimating the fuel pressuredrop based additionally on a half period of the inter-injection periodbefore injecting the fuel. The method further comprises estimating thefuel pressure drop based additionally on a half period of theinter-injection period after injecting the fuel. The method furthercomprises estimating a mass of fuel injected based on the estimated fuelpressure drop. The method further comprises adjusting a pressure in thefuel rail to a predetermined pressure before injecting the fuel. Themethod includes where the pressure is adjusted via adjusting a fuelpump. The method further comprises deactivating the fuel pump after thepressure in the fuel rail is adjusted to the predetermined pressure.

The method of FIG. 5 also provides for a method for operating a fuelinjector, comprising: estimating a fuel pressure drop in a fuel rail dueto injecting a fuel via a fuel injector according to a portion of aninter-injection period where pressure samples are not applied toestimate the fuel pressure drop; and adjusting fuel injectedsubsequently via the fuel injector based on the estimated fuel pressuredrop. The method includes where the inter-injection period is afterinjecting the fuel. The method further comprises estimating the fuelpressure drop in further response to an average fuel pressure beforeinjecting the fuel, an average fuel pressure after injecting the fuel, aslope of fuel pressure during an inter-injection period before injectingthe fuel, and a slope of fuel pressure during the inter-injection periodafter injecting the fuel. The method includes where the inter-injectionperiod is before injecting the fuel. The method further comprisesestimating a mass of fuel injected based on the estimated fuel pressuredrop.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The control methods and routines disclosed herein may be stored asexecutable instructions in non-transitory memory and may be carried outby the control system including the controller in combination with thevarious sensors, actuators, and other engine hardware. The specificroutines described herein may represent one or more of any number ofprocessing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various actions,operations, and/or functions illustrated may be performed in thesequence illustrated, in parallel, or in some cases omitted. Likewise,the order of processing is not necessarily required to achieve thefeatures and advantages of the example embodiments described herein, butis provided for ease of illustration and description. One or more of theillustrated actions, operations and/or functions may be repeatedlyperformed depending on the particular strategy being used. Further, thedescribed actions, operations and/or functions may graphically representcode to be programmed into non-transitory memory of the computerreadable storage medium in the engine control system, where thedescribed actions are carried out by executing the instructions in asystem including the various engine hardware components in combinationwith the electronic controller.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein.

As used herein, the term “approximately” is construed to mean plus orminus five percent of the range unless otherwise specified.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

The invention claimed is:
 1. A method for operating a fuel injector,comprising: estimating a fuel pressure drop in a fuel rail due toinjecting a fuel via a fuel injector according to an average fuelpressure before injecting the fuel, an average fuel pressure afterinjecting the fuel, a slope of fuel pressure during an inter-injectionperiod before injecting the fuel, and a slope of fuel pressure during aninter-injection period after injecting the fuel; and adjusting fuelinjected subsequently via the fuel injector based on the estimated fuelpressure drop.
 2. The method of claim 1, further comprising estimatingthe fuel pressure drop based additionally on a half period of theinter-injection period before injecting the fuel.
 3. The method of claim2, further comprising estimating the fuel pressure drop basedadditionally on a half period of the inter-injection period afterinjecting the fuel.
 4. The method of claim 1, further comprisingestimating a mass of fuel injected based on the estimated fuel pressuredrop.
 5. The method of claim 1, further comprising adjusting a pressurein the fuel rail to a predetermined pressure before injecting the fuel.6. The method of claim 5, where the pressure is adjusted via adjusting afuel pump.
 7. The method of claim 6, further comprising deactivating thefuel pump after the pressure in the fuel rail is adjusted to thepredetermined pressure.